Selective prion protein binding to synaptic components is modulated by oxidative and nitrosative changes induced by copper(II) and peroxynitrite in cholinergic synaptosomes, unveiling a role for calcineurin B and thioredoxin.

Choline acetyltransferase (ChAT) and choline transport are decreased after nitrosative stress. ChAT activity is altered in scrapie-infected neurons, where oxidative stress develops. Cellular prion protein (PrPc) may play a neuroprotective function in participating in the redox control of neuronal environment and regulation of copper metabolism, a role impaired when PrPc is transformed into PrPSc in prion pathologies. The complex cross-talk between PrPc and cholinergic neurons was analyzed in vitro using peroxynitrite and Cu2+ treatments on nerve endings isolated from Torpedo marmorata, a model of the motoneuron pre-synaptic element. Specific interactions between solubilized synaptic components and recombinant ovine prion protein (PrPrec) could be demonstrated by Biacore technology. Peroxynitrite abolished this interaction in a concentration-dependent way and induced significant alterations of neuronal targets. Interaction was restored by prior addition of peroxynitrite trapping agents. Cu2+ (in the form of CuSO4) treatment of synaptosomes triggered a milder oxidative effect leading to a bell-shaped increase of PrPrec binding to synaptosomal components, counteracted by the natural thiol agents, glutathione and thioredoxin. Copper(II)-induced modifications of thiols in several neuronal proteins. A positive correlation was observed between PrPrec binding and immunoreactive changes for calcineurin B and its partners, suggesting a synergy between calcineurin complex and PrP for copper regulation.

Inhibition of acetylcholine synthesis and tyrosine nitration induced by peroxynitrite are differentially prevented by antioxidants.

Evidence of an overload of reactive oxygen species and peroxynitrite, a derivative of nitric oxide, in sporadic amyotrophic lateral sclerosis suggests that peroxynitrite could impair cholinergic functions. Because of the impossibility of obtaining synaptosomes from vertebrate neuromuscular junctions, we used cholinergic synaptosomes purified from Torpedo marmorata electroneurons to characterize the defects triggered by peroxynitrite in more detail. Addition of peroxynitrite or its donor 3-morpholinosydnonimine abolished high-affinity choline uptake and synthesis of acetylcholine from acetate. T. marmorata choline acetyltransferase (ChAT) was impaired to the same extent as bovine brain ChAT. A hallmark of peroxynitrite action is the nitration of tyrosine residues in proteins. Peroxynitrite induced a concentration-dependent appearance of nitrotyrosines in several neuronal proteins from synaptosomes and, more readily, from synaptic vesicles. Peroxynitrite also triggered tyrosine nitrations in purified ChAT. Peroxynitrite-dependent nitrations were impaired when synaptosomes were pretreated with thioreductants (glutathione, N-acetyl cysteine, dithiothreitol) or antioxidants (uric acid, melatonin, bovine serum albumin, desferrioxamine). Deleterious effects of peroxynitrite on choline transport and ChAT activity were prevented by the thioreductants but only partially by the antioxidants, suggesting a mechanism other than tyrosine nitration, which may involve cysteine oxidation. Further development of protective agents acting on choline transport and on ChAT activity may offer interesting therapeutic possibilities with respect to cholinergic dysfunction occurring in neurodegenerative diseases.